1. Technical Field
The following disclosure relates to a system and method for monitoring macroscopic tissue modifications during an electrosurgical procedure, and more particularly to a system and method that quantifies the progress of tissue thermal damage and dehydration using optical monitoring.
2. Description of Related Art
Electrosurgical forceps use a combination of mechanical pressure and electrical energy to effect hemostasis, by heating tissue and blood vessels to coagulate, cauterize and/or seal tissue. By controlling the power, frequency and duration of the electrical energy delivered to the tissue, a surgeon can cauterise, coagulate, desiccate and/or slow bleeding. However, the delivered energy must be controlled in real-time as a function of the tissue state so that a reliable and reproducible surgical effect is generated.
To resolve the issues above and other issues relevant to coagulation and other tissue treatments, Valleylab Inc. (a division of Tyco Healthcare LP) has developed a technology called vessel or tissue sealing. Electrosurgical vessel sealing is fundamentally different from the process of coagulating vessels. For the purposes herein, “coagulation” is defined as a process of desiccating tissue wherein the tissue cells are ruptured and dried. Vessel sealing is defined as a process of liquefying collagen in tissue, so that it forms a fused mass with limited demarcation and capable of joining opposing tissue structures to seal a large vessel.
It is known in the art that the radio frequency (RF) energy delivery, the distance between jaw members in the sealing device and the pressure exerted by the jaw members must be controlled. In this way, the optimum tissue transformations leading to a seal can be generated, and hence a reproducible reliable seal can be achieved.
Two macroscopic effects that are induced in tissue during the RF tissue fusion process are thermal damage and dehydration. For the purposes herein, the term “thermal damage” is used to describe any bio-structural alteration of the tissue induced by heat. Thermal damage generally includes several biophysical modifications of the tissue that can ultimately lead to tissue death or denaturation—the loss of tridimensional protein structure.
The energy delivered to the tissue during an electrosurgical procedure and the consequent tissue transformations must be controlled and terminated so that a reliable seal is achieved. Historically, it was the responsibility of the surgeon to control and terminate the delivery of energy when the desired effect was produced. The experience of the surgeon was therefore of paramount importance. In the late 1980s, feedback controlled energy sources were introduced, in an effort to eliminate the need for empirical operation. For example, modifications to the tissue electrical impedance have been used as a feedback parameter in RF tissue fusion. Similarly, modifications to the optical properties of the tissue have been suggested to measure transformations induced by laser processing. Each of these methods has some drawbacks.
For example, impedance is often used to control the delivery of RF energy during tissue fusion, because it is relatively easy to measure and because dehydration is believed to reduce conductivity and, hence, increase impedance during the final stage of the fusion process. However, hydration does not completely correlate to impedance. As a result, impedance tends to be a less useful control parameter for the overall tissue sealing process.
Optical spectroscopy has the potential to provide more detailed information on the overall state of the tissue, since it allows information to be gathered on both the tissue structure and the tissue's biochemical makeup. In this case, there are much more significant meteorological challenges, since the detectable signals are generally very weak. Further, algorithms are typically required to extract directly relevant information about the tissue-state from the raw optical signals.
Various prior art patents have proposed the use of optical measurements to control the delivery of energy during an electrosurgical procedure, e.g., U.S. Pat. Nos. 5,762,609; 5,769,791; 5,772,597; and 5,785,658 to Benaron. These references disclose that signals can be measured either at or inside the surface of the tissue and that spectroscopy may be utilized in transmission or in reflection to monitor the signal. However, experiments show that the very large changes in scattering that occur in tissue can cause the signal detected by either method to be effectively extinguished during different stages of a thermal process, so that neither method on its own can provide continuous feedback. The systems proposed by Benaron also use raw optical parameters to control the electrosurgical generator, rather than extracted parameters such as thermal damage and tissue hydration.